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TOPIC: 72 Mercury115 Compression test

72 Mercury115 Compression test 1 year 2 weeks ago #133937

I have a 72 115 mercury. I am taking the powerhead off to replace the lower cowling. I tested the compression before taking apart, and got 105 to 110 psi on all cylinders. 5 lb max variation. I am wondering if that may be good, or engine teardown needed. What are your guys thoughts. I also have a couple 150 inlines, both 77's. I am going to test them. I am trying to put together a good engine for my 77 Glastron Carlson CV16. Is the basic 115 powerhead compatible with the 150's.

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72 Mercury115 Compression test 1 year 2 weeks ago #133954

The 1972 1150 power head is not compatible as a unit with the 1500-6.
The crankshaft, rods, bearings, stator, switch-box & coil, and lower unit will cross, but that's about it.
A completely different bolt pattern between the power-head & the exhaust adapter plate, plus a different drive shaft housing (DSH) eliminate any hopes of marrying the early 1150 to the 1500 adapter plate & DSH.
In 1972, the 1400-6, was the first inline-6 to shift to the later exhaust configuration.
In 1973-1988, all inline-6 models shared lots of components that could be easily swapped around.
The cool part about a 1972 1150 is that armed with a few key parts it can easily be converted to a 1350, which is the badest of the oval port inline-6 Mercs. (IMHO of course)

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72 Mercury115 Compression test 1 year 1 week ago #133957

What about the compression? One manual I have says anything over 100 psi is acceptable. I did not have the carburetors open at time of the test, maybe this affected it. I am trying to put this boat together on the cheap, so If I don't have to tear down the powerhead, I may use it. I do have 2 matching 77 150's that I can use. One that I was told had no compression? obviously untrue, as I t ran, but would not power up. By the way, I picked both the 115 and a 150 up at a local scrap metal yard. Both powerheads look very good, but have broken lower cowels. My Glastron is rated for 125 HP, and is a 77 model, so 1`50 could be a better match. Thanks for the info, I should have posted this in the Mercury forum. Thanks again.

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72 Mercury115 Compression test 1 year 1 week ago #133964

I hope the good DR. will agree with me, but I have been told anything over 100 # and consistent numbers through all cylinders is good. You should get a lot of use out of it before you need a rebuild. Give or take 5# between cylinders is not a problem.

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